A. Field of the Invention
The invention relates to a gear shifting mechanism having a lever arm, and a pawl member in engagement with a geared member with gear teeth for limiting movement of the lever arm to incremental step-wise movement.
B. Description of the Related Art
Multiple speed bicycles have become very common recently. Multiple speed bicycles include, for instance, racing bicycles, street bicycles and mountain bicycles. Multiple speed bicycles typically have at least one gear derailleur and the lever mechanism for manipulating the gear derailleur. It should be understood that there are also multiple speed bicycles having gear changing mechanisms that use mechanisms other that a gear derailleur for changing a gear ratio on the bicycle.
The lever mechanism for effecting the change of the gear ratio on a bicycle is often referred to as a gear shifting mechanism. One gear shifting mechanism includes a lever arm supported for pivotal movement on a base attached to a bicycle frame. The lever arm attaches to a cable, the cable being connected to a gear derailleur or similar gear ratio changing mechanism. The lever arm is moved by a bicyclist to an approximate position thus moving the cable and correspondingly moving the gear ratio changing mechanism. The lever arm is moved to a position corresponding to the desired gear ratio. The lever arm movement is restricted by, for instance, friction which is great enough to keep the lever arm in position, but not so great as to prevent a user from easily changing gear ratios. The positioning of the lever arm to change gears is not precise.
In recent years, however, gear shifting mechanisms have developed into precision mechanisms configured to allow the lever arm to lock into a plurality of positions, each position corresponding to a gear ratio in accordance with the gear changing characteristics of a gear derailleur or similar gear ratio changing mechanism. For instance, in FIG. 1, a prior art gear changing mechanism 1 is shown.
In the prior art gear changing mechanism 1, a base (not shown) attaches the gear changing mechanism to the frame or handlebar of a bicycle (not shown) or to a brake lever mechanism on the handlebar of a bicycle (not shown). The base (not shown) connects to a disk member 2. The disk member 2 is formed with a cable shield retainer 2a which engages and holds the cable shield (not shown) through which an inner cable extends.
A shaft member 3 attaches to the disk member 2 via pins 3a which extend through holes 2b in the disk member 2. The pins 3a may be spot welded to the plate member 2 or punched so that they are deformed within the holes 2b. The shaft member 3 is formed with an indented shaft 3b having threads 3c formed on an outer periphery thereof.
A handle 4 is formed with a lever arm 5, a central bore 4a, protrusions 4b and a cable retainer hole 4c. The indented shaft 3b extends through the central bore 4a when the mechanism 1 is fully assembled. A positioning disk 6 is formed with two opposing indents 6a, a plurality of opposing recesses 6b and a central bore 6c. The indented shaft 3b extends through the bore 6c when the mechanism 1 is fully assembled. The indents 6a fit around the protrusions 4b when the mechanism 1 is fully assembled. A fixed plate 7 is formed with an indented central aperture 7b and two ball holes 7a. One ball 8 is disposed in each of the ball holes 7a. The diameter of the balls 8 is greater than the thickness of the fixed plate 7. A retainer plate 9 is also formed with an indented central bore 9a through which the indented shaft 3b extends. The retainer plate 9 is also formed with two ball confining protrusions 9b positioned to retain the balls 8 in the holes 7a in engagement with the positioning disk 6. A threaded nut 10 screws on to the indented shaft 3b to hold the mechanism 1 together. In usage, a cable (not shown) would extend through the hole 2c in the cable shield retainer 2a and extend through the cable retainer hole 4c.
Movement of the lever arm 5 causes the cable (not shown) to move. When fully assembled, the mechanism 1 allows the lever arm 5 to be rotated about the shaft member 3. The positioning disk 6 rotates with the lever arm 5 due to the engagement of the protrusions 4b with the two opposing indents 6a. However, the central bores 7b and 9a are confined by the indented shaft 3b such that they cannot rotate with respect to the shaft member 3. As the lever arm 5 is rotated, the positioning disk 6 is rotated therewith, but the balls 8 are confined to engage the surface of the positioning disk 6 by the holes 7a and the ball confining protrusions 9b. The balls 8 are able to engage and extend into any of the recesses 6b. When the balls 8 are engaged in one pair of opposing recesses 6b, the lever arm 5 is locked gently into a predetermined position.
The lever arm 5 is confined to incremental step-wise movement about the shaft member 3 by the interaction of balls 8 with the recesses 6b. In this manner the lever arm 5 may control the shifting of gears on a bicycle.
There are several disadvantages to the above design, shown in FIG. 1. One disadvantage is that there are a large number of parts making manufacturing expensive. Another disadvantage is that several of the parts in the design shown in FIG. 1 require fine machine working during manufacturing. For instance, a portion of the shaft must be indented and must have threads formed thereon. Further, each of the plates 7 and 9 is formed with a non-circular bore which is also formed using relatively expensive manufacturing procedures.